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An insufficient number or quality of red blood cells in the fetal circulatory system to adequately carry oxygen to the cells and organs of the fetus.
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GUIDELINE OBJECTIVE(S)
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Review important etiologies of fetal anemia; examine different clinical approaches to identifying at-risk or already affected fetuses; compile recommendations for antenatal surveillance, fetal diagnostic and therapeutic interventions, delivery planning, and immediate postnatal management.
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Fetal anemia is defined as a hematocrit or hemoglobin concentration more than two standard deviations below the mean for a given gestational age. It can develop as the result of three general causes: increased fetal red blood cell (RBC) destruction, decreased fetal RBC production, or fetal blood loss. There are several different scenarios in which fetal anemia may be detected in the antenatal period (Table 4.1). Anemia leads to decreased oxygen delivery to tissue, but mild to moderate anemia is generally well tolerated by the fetus and can resolve without sequelae. However, if the anemia becomes more severe, it can lead to fetal compensatory responses, resulting in the development of fetal hydrops and/or death. Unfortunately, in the antenatal period, most clinical signs of fetal anemia only become apparent at this severe stage. Thus most diagnostic efforts have focused on the surveillance of pregnant women identified as carrying fetuses at particular risk of developing anemia.
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MAJOR RECOMMENDATIONS
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Management of the At-Risk Mother
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Positive Maternal Antibody Screen
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The presence of maternal red blood cell (RBC) antibodies, also known as alloimmunization, may lead to fetal hemolysis with subsequent anemia depending on the degree of antigenicity and the amount and type of antibodies involved. Therefore, a maternal antibody screen should be performed on all women at their first prenatal visit. If the antibody screen is positive, the detected antibody should be identified and characterized for its potential to cause fetal hemolytic disease (Figure 4.1). If the identified antibody has never been associated with fetal hemolysis, no further evaluation is necessary. However, if the identified antibody is clinically significant, the next step is to determine paternal antigen carrier status. If paternal testing is not possible or if it is positive, serial antibody titers (indirect Coombs test) should be followed, with further testing only if a critical threshold is reached. Titer values are conventionally reported as the integer of the greatest tube dilution with a positive agglutination reaction. A critical titer is defined as the titer associated with a ...